What it is
A starchy tropical root that feeds a good part of the planet — boiled, roasted, or ground to flour. Tapioca is the starch washed out of it.
Why your biology objects
An ancestral tuber starch, exactly the carb the thesis endorses — energy-dense, with vitamin C and some resistant starch when cooled. The real footnote is preparation: cassava carries cyanogenic glycosides (linamarin) that bitter varieties must have soaked, fermented or cooked out. Properly processed it's a staple; raw and bitter it's dangerous. The pot is part of the food.